• those that actually store data:
  • back-bdb
  • back-hdb
  • back-ldif (since 2.3)
  • (back-ldbm is no longer supported as of 2.4)
• those that proxy other data storage systems:
  • back-ldap
  • back-meta
  • back-passwd
  • back-relay (since 2.3)
  • back-sql
• those that dynamically generate the data:
  • back-config (since 2.3)
  • back-dnssrv
  • back-monitor
  • back-null
  • back-perl
  • (back-tcl is no longer supported as of 2.2)
  • back-shell

The borderline between the categories may not be very well defined; for instance, back-dnssrv may be listed in the second category as well, since it essentially proxies DNS info, and back-monitor is a means to publish internally generated data in LDAP form rather than a storage system.
ando@sys-net.it, hyc@openldap.org

Builtin backends: use the

        --enable-<backend>=mod

Custom backends: simply write a module that implements the backend functionalities and add a function

        static BackendInfo bi;

        int
        init_module( int argc, char *argv[] )
        {        
                memset( &bi, '\0', sizeof( bi ) );
                bi.bi_type = "custom" ;
                bi.bi_init = custom_back_initialize;
                backend_add( &bi );
                return 0;
        }

What is a backend?

What is a database?

Backend specific answers and subcategories:
The BDB/HDB backend (How do I setup/configure back-bdb/back-hdb?)
The LDBM backend
The LDAP backend (How do I setup/configure back-ldap?)
The passwd backend (How do I setup/configure back-passwd?)
The SQL backend (How do I setup/configure back-sql?)
config backend configuration
the monitor backend (How do I configure the cn=monitor backend)